FIG. 36A is a block diagram of conventional inertia sensor 1. Inertia sensor 1 includes three piezoelectric elements 2 for detecting an inertial force, switching element 3 implemented by field-effect transistors, and amplifier circuit 4 implemented by an operational amplifier. In order to detect inertial forces in three directions perpendicular to each other, inertia sensor 1 extracts outputs from three piezoelectric elements 2 as a single output by switching the switching elements 3 between piezoelectric elements 2 and amplifier circuit 4. As described above, switching elements 3 are used to sequentially switch and extract the outputs from piezoelectric elements 2, and constitute a detection circuit in which multi-axial detection can be performed with single amplifier circuit 4.
In inertia sensor 1, currents output from piezoelectric element 2 become small as inertia sensor 1 has had a small size. In order to detect intended signals, based on such small output currents, amplifier circuit 4 has an amplification performance to amplify intended signals at a gain as large as possible while producing small noises.
FIG. 36B is a block diagram of amplifier circuit 4. In order to obtain the above-described amplification performance, amplifier circuit 4 converts a current to a voltage and has a frequency characteristic of a low-pass filter.
Amplifier circuit 4 has input terminal 5, input terminal 6 connected to a reference potential, and output terminal 4a which is connected to input terminal 5 via feedback capacitor 7 and feedback resistor 8 to constitute feedback loop 9.
A conventional inertia sensor similar to inertia sensor 1 is disclosed in PTL 1.
When the output from inertia sensor 1 which has a switching structure with switching element 3 is amplified, output characteristics or an S/N ratio may deteriorate in inertia sensor 1 shown in FIG. 36A.